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FlexRay and Automotive Networking
Future
Chris Quigley
Warwick Control Technologies
Presentation Overview

High Speed and High Integrity Networking

Why FlexRay? CAN Problems

Time Triggered Network Principles

Time Triggered Protocol Candidates

FlexRay protocol and Applications: BMW, Audi, SAPECS

Other Emerging Protocols and Standards

Summary
2
Why FlexRay?
CAN is extremely cost effective and powerful technology
However, for more intensive applications, it is reaching its
limit
CAN Problems

Unpredictable Latency (unless you buy into expensive solutions)

Undetected bit errors (1.3 x 10-7)

Bandwidth Limitation – 500Kbit/s typical maximum (1Mbit/s possible)

Too expensive for intelligent sensors and actuators

Emerging X-by-Wire and high integrity applications

Complicated automotive architectures
•
More design effort
•
Weight increase from additional ECUs, gateways, connectors
3
Why FlexRay? – CAN Latency
Typical CAN bus characteristic –
unpredictable latency
Message
Latency
Typical TT network characteristic –
predictable latency
Message
Latency
Bus Load
Bus Load
4
Why FlexRay? – Complicated Architectures
CAN de-facto standard but problems include:
Wiring running the length of the vehicle
Too many ECUs – design complexity
Not robust enough for future X-by-wire
5
Emerging Networks - Nodal Costing
400M
IDB-1394
(Firewire)
Bit rate
MOST50
25M
(Twisted
Pair)
10M
FlexRay II
TTP/C
MOST25
(Optical)
FlexRay 2.1
1M
CAN / TTCAN
Safe-by-Wire
20K
LIN
0.5
2.5
5.0
Relative Cost
6
Alternative Architecture
Alternative architecture possible due
to the new technologies
Features (Chassis control only):
Based on FlexRay and LIN
LIN for sensors
FlexRay for high speed integration
Shorter wiring to local ECUs
Reduced design complexity
Generic ECUs – Reduced cost
7
Network Architecture of Future
- Many proposed uses of FlexRay
 FlexRay
 High speed backbone
 X-by-Wire
 Airbag deployment
 LIN Sub Bus:
 Doors
 Seats etc.
 CAN/TTCAN –
Applications:
 Powertrain/body
 TTCAN deterministic
powertrain
 MOST
Infotainment
8
Time Triggered Network Principles
Communication based on Slots or Windows of time
Determinism

Message transmission time known
Schedule defined by a Matrix

m Windows x n Cycles
Message Scheduling Techniques:

TDMA

Mini-slotting
9
Time Triggered Network Principles
Time Triggered Matrix for Schedule
Increasing Window or Slot Number
Increasing
Cycle
Number
Message1
Message2
Message4
Message5
Message6
Message1
Message3
Free Window
Free Window
Free Window
Message1
Message2
Free Window
Free Window
Free Window
Message1
Message3
Message4
Free Window
Free Window
Message1
Message2
Free Window
Free Window
Free Window
10
Time Triggered Network Principles
Time Division Media Access Scheduling Technique
In general:
Messages are always transmitted in the
appropriate slot
Increasing Window Number
Increasing
Cycle
Number
Message1
Message2
Message4
Message5
Message6
Message1
Message3
Free Window
Free Window
Free Window
Message1
Message2
Free Window
Free Window
Free Window
Message1
Message3
Message4
Free Window
Free Window
Message1
Message2
Free Window
Free Window
Free Window
11
Time Triggered Network Principles
Mini-Slotting Scheduling Technique
Communication Cycle Length
m+1
Cycle 0
Slot ID m
Cycle 1
m
m+1
Cycle 2
m
m+1
m+2
Slot ID m+2
m+2
Duration of Mini-Slot depends upon whether or not frame transmission takes place
If transmission does not take place, then moves to next mini-slot
Message transmission will not take place if it cannot be completed within the Cycle
Length
12
Time Triggered Protocol Candidates
Candidates that were considered include:

Time Triggered CAN

Byteflight

TTP

FlexRay
13
Time Triggered CAN (TTCAN)
TDMA message scheduling techniques and Arbitration
Windows


1Mbit/s

Single channel

Twisted Pair CAN Physical layer

No commercial examples
14
Byteflight

Mini-slotting message scheduling technique

10Mbit/s

Single channel

8 bytes of data payload
BMW 7-Series (2001) – only production example

Airbag deployment, seatbelt restraint

Throttle and shift-by-wire
15
Time Triggered Protocol (TTP)

TDMA message scheduling technique

25Mbit/s and beyond

Dual channel for redundancy or faster transfer

244 byte data payload

No automotive commercial examples
Commercial examples:

Boeing 787 flight controls

Off highway drive-by-wire
16
FlexRay

TDMA and mini-slotting message scheduling technique

10Mbit/s

Dual channel for redundancy or faster transfer

254 byte data payload
Commercial examples:

BMW 2006 X5 for chassis controls

Audi next generation A8

Flight controls in development
17
FlexRay Compared to CAN
CAN
FlexRay
Message IDs (bits)
11 and 29
11
Data payload (bytes)
8
254
Network Architecture
Bus
Bus, Star, Mixed
CRC
15 bit
15 bit Header CRC
24 bit Trailer CRC
Bus Access
CSMA-CD-NDBA
TDMA and mini-slots
Bit rate
Max. 1Mbit/s
2.5, 5, 10Mbit/s
Bus Guardian
None
Specified, not developed
Physical Layer
Twisted Pair
Twisted Pair
Semiconductor Support
Many
Many in development
18
FlexRay Frame Format
RTR
‘0’ = Data
‘1’ = Request
SOF
Reserved
(= ‘00’)
CRC Delimiter
(1)
Acknowledge Frame
(2)
DLC (4)
Standard CAN
Identifier
(11)
Data
(0 - 8 Bytes)
CRC
(15)
End of
Frame
(7)
19
FlexRay and CAN Network Topologies
CAN Topologies
• Linear Passive Bus:- Similar to
current CAN bus
FlexRay Numerous
topologies include:• Passive Star:- Low cost star
• Active Star:- Fault tolerant star
• Linear Passive Bus:- Similar to
current CAN bus
• Dual Channel Bus:- Dual redundancy
• Cascaded Active Star:- Multiple
couplers
• Dual Channel Cascaded Active Star:• Additional safety
• Mixed Topology Network:-
• Mixture of Star and Bus topologies
20
FlexRay Network Access
Time Triggered (64 cycles of
continuous schedule)
CAN Bus Access – CSMA-CD-NDBA

NDBA = Non Destructive Bitwise Arbitration
S OF
Node A
ID 1 4 9 3
t1
FlexRay Network Access - static &
dynamic segments

Static = Time Division Media Access

Dynamic = Mini-slotting
t2
R
D
R
Node B
ID 1 5 0 1
D
R
Node C
ID 2 0 1 3
D
R
Bus
ID 1 4 9 3
D
21
FlexRay Static Segment
Frames of static length assigned uniquely to slots of static duration
• Frame sent when assigned slot matches slot counter
BG protection of static slots (when it is available)
22
FlexRay Dynamic Segment
Dynamic bandwidth allocation
• per node as well as per channel
Collision free arbitration via unique IDs and mini-slot counting
• Frame sent when scheduled frame ID matches slot counter
No BG protection of dynamic slots
23
Communication Example (3 Cycles)
Communication Cycle Length
Static Segment
Dynamic Segment
Cycle 0
Static Slot 0
Static Slot 1
Dynamic Slot ID m
Cycle 1
Static Slot 0
Static Slot 1
m
m+1
Cycle 2
Static Slot 0
Static Slot 1
m
m+1
m+1
m+2
Dynamic Slot ID m+2
m+2
Duration of Dynamic Slot depends upon whether or not
frame tx or rx takes place
Another 61 cycles and
then back to Cycle 0
again
Each mini slot contains an Action Point (macroticks) when
transmission takes place
If transmission does not take place, then moves to next
mini-slot
24
Node Architecture - Bus Guardian
CAN
None specified, could use proprietary
implementation
FlexRay
Bus Guardian – specified but not
developed
• BD – Bus Driver
• Electrical Physical layer
• BG – Bus Guardian
• Protects message schedule
• Stops “Babbling Idiot” failure
25
FlexRay Physical Layer
FlexRay – Twisted Pair (22metres@ 10Mbit/s)
CAN – Twisted Pair (40metres@ 1Mbit/s)
Electrical signals differ
Differential voltage uBus = uBP - uBM
Idle-LP is Power Off situation. BP and BM at GND.
Idle is when no current is drawn but BP & BM are biased to the same voltage level
Data_1, BP at +ve level, BM at -ve level, Differential = +ve
ISO 11898 CAN High Speed
Data_0, BM is +ve level, BP is -ve level, Differential = -ve
Recessive
Dominant
Recessive
3.5 V
CAN_High
Vdiff
2.5 V
VDiff
2V
0V
1.5 V
CAN_Low
26
FlexRay Voltage Levels – In Practice
The FlexRay PL has a buffer supplied by VBuf
(typically ~5v)
The idle level is half VBuf

Typically around 2.5 volts
At startup - Shows rise from Idle_LP to Idle
Red shows BP
Green shows BM
27
FlexRay Application: BMW
 Latest BMW X5
5 ECUs for Adaptive Drive – Electronic
damper control


Wheel located ECUs

Management unit acts as Active Star

Audi have announced new A8 with FlexRay
SAPECS (2004 to 2007)
(Secured Architecture & Protocols for Enhanced Car
Safety)
Objectives
• Capture Requirements of :• information around vehicle
• telematic information between vehicle & infrastructure
• FlexRay Demo
• Develop and integrate FlexRay IP for demo
• Demo of power train control
• Analysis / Qualification tool for displaying data
• Qualification standards for systems
• Review of current
• Suggestion of new procedures and tools for qualification
29
SAPECS - Partner Inputs
Company
Contribution
AMI Semiconductors
FlexRay physical layer development
Atmel Nantes
FlexRay microcontroller with fail-safety
functionality development
Ayrton Technology
FlexRay software stack development
CS
Capture requirements for vehicle &
telematic information
Valeo
Engine management demonstrator
Warwick Control
Design, Analysis and automatic
FlexRay stack configuration tools
30
SAPECS FlexRay Demonstrator
31
SAPECS FlexRay Demonstrator
Electronic Throttle Motor controlled by Electronic Pedal Sensor via the Engine ECU
ECUs connected to a Dual Channel FlexRay bus
Distributed Architecture with THREE calculators:

Pedal
•


3 ECUs - majority voter calculates position at Engine ECU
Throttle
•
receives new position from Engine ECU
•
turns position info into H bridge control data.
Engine Management (Main)
•
Performs standard engine management along with throttle control
•
Receive pedal position data from the three Pedal ECUs to perform the majority voter
strategy.
•
Transfers the new position to the Throttle ECU.
32
SAPECS FlexRay Communication –
Development Process
Validation
Requirements
FlexRay database
(Prototype
of future
NetGen, XEditor)
FlexRay
Network
Analyser
XML
Configuration
File
FlexRay
Planning
Tool
Code Test
Design
FlexRay
Interface
Card
FlexRay Code
Configuration
Tool
C- Coding
Node
Under
Development
FlexRay
Node
FlexRay
Node
FlexRay
Node
33
Other Emerging Network Technologies
Safe-by-Wire Plus

Safe-by-Wire Plus consortium formed in February 2004

Automotive safety bus for occupant safety applications (e.g.
airbag deployment and seat belt restraint)

Safe-by-Wire Plus has variable bus speeds of 20, 40, 80 or 160
kbps

Expected to have a similar nodal cost comparable to CAN

The application of the Safe-by-Wire protocol is narrow and
therefore is not suitable for general network service
34
Emerging Standards
Network data exchange:
CANdb

Vector proprietary
LDF (LIN Description Files)

Open standard

LIN only
FIBEX

New open ASAM standard

CAN, LIN, MOST, FlexRay

For diagnostics/analysis tools
AUTOSAR (CAN, LIN, MOST, FlexRay)

For ECU designers
35
Summary and Outlook
CAN

original aim: reduction wiring harness complexity, size and weight

However, successful adoption has allowed integration of many more ECUs

Led to more wiring, more CAN buses, more gateways etc.
FlexRay

off-the-shelf technology available for applications in which CAN performance
has limitations and has been compared with CAN

FlexRay implemented in the BMW X5 plus numerous other emerging
applications

Likely to become de-facto standard for X-by-Wire and future high speed
networking

Protocol features likely to evolve further

Danger is that FlexRay will allow the growth in vehicle electronics to explode

Extremely complex when compared to CAN!!!!!!!!
36